An antenna in a transmitting configuration transforms electronic signals, such as the electronic signals received from a radio, into electromagnetic signals for propagation through the air. Conversely, an antenna in a receiving configuration receives electromagnetic waves from the air and transforms the electromagnetic waves into electronic signals, such as for provision to a radio. A band pass filter is generally required to be disposed in series with an antenna to permit only desired signal frequencies to pass therethrough. The antenna and the band pass filter are generally physically separate from one another and connected by a transmission line, for example, a 50 ohm transmission line.
An antenna array generally includes dual-polarized antenna elements positioned with a half-wavelength spacing. Each polarization of the dual-polarized antenna elements of an antenna array allows an independent channel to be transmitted and received, thereby effectively doubling the bandwidth of the antenna array. A fully active antenna array having multiple antenna elements with half wavelength spacing can provide fully digital beam forming along with multiple input multiple output (MIMO) functionality. In this scenario, the fully active antenna array may include multiple independent antenna elements with half wavelength spacing to increase the capacity of the antenna array. However, a band pass filter is still required for each of the multiplicity of antenna elements of the fully active antenna array.
As such, a multi-mode antenna includes a plurality of antenna elements, each having a respective band pass filter with a half wavelength spacing between the antenna elements, thereby imposing a requirement for a substantial number of band pass filters in some circumstances. However, the provision of a plurality of antenna elements with their respective band pass filters with a half wavelength spacing may be challenging, particularly when endeavoring to concurrently maintain adequate port isolation, a low envelope correlation coefficient (ECC), a low insertion loss (and a corresponding high efficiency) and a similar radiation pattern for each antenna element in order to allow for multi-channel beam forming.